The invention concerns a method of manufacturing a lift transmitting component, particularly for a gas exchange valve train or a fuel pump drive of an internal combustion engine, with the lift transmitting component comprising a housing, a bearing pin fixed in a reception bore of the housing and a roller mounted through a sliding or a rolling bearing on the bearing pin, with the bearing pin being core-hardened over an entire axial length to a core hardness of at least 650 HV (Vickers hardness), and pin ends of the core-hardened bearing pin being radially widened relative to the reception bore for enabling a connection of the bearing pin to the housing through positive engagement.
A lift transmitting component configured as a roller tappet for activating a tappet push rod of a gas exchange valve of an internal combustion engine with a bottom camshaft is known from U.S. Pat. No. 5,099,807. The roller tappet comprises a cam-activated roller, mounted through a rolling bearing on a bearing pin that is fixed through radially widened pin ends both by positive engagement and by force-locking in a reception bore of the tappet housing. The radial deformation of the pin ends is effected by gyratory swaging or calking and the calked material of the bearing pin is displaced in the form of a circular ring into a chamfer at the opening of the reception bore.
An alternative manner of fixing the bearing pin in the housing is disclosed, for example, in U.S. Pat. No. 4,628,874. In addition to a roller tappet, this document also discloses a lift transmitting component configured as a roller finger lever. In both cases, the bearing pin for the roller is fixed in the reception bore of the housing concerned by the fact that the material of the front ends of the bearing pin is displaced by a calking method radially outwards into a circumferential undercut situated within the reception bore.
Undercuts of the aforesaid type are also proposed for a roller tappet disclosed in U.S. Pat. No. 5,385,124. However, these undercuts do not serve to receive calked material of the bearing pin but for the reception of circlips that serve as positive engagement axial stops for the non-deformed pin ends of a bearing pin that is float-mounted in the reception bore.
A common feature of all the lift transmitting components proposed in the cited documents is that, with the aim of achieving wear resistance, their bearing pins are hardened in the region of their roller raceways. But if a bearing pin is calked, it is imperative for its front ends to be adequately soft in view of the material flow that is concomitant with the swaging or calking process. Such a bearing pin with non-uniform hardness values along its length, however, can only be realized through complex and, thus, cost-intensive heat treating methods. A further drawback of a bearing pin whose ends have only a low hardness arises from the fact that its calked pin ends must be fixed in the reception bore not only by positive engagement but also by force-locking. The reason for this is that the soft pin ends of a bearing pin that is not fixed by force-locking in the reception bore and is made to rotate by the friction forces of the rotating roller, could be subjected to contact friction with the housing on their periphery, so that they could suffer a loss of their axial securing function and thus shear off. A fixing of the bearing pin in the reception bore not only by positive engagement but also substantially by force-locking can pose a problem in cases in which the housing of the lift transmitting component has to meet special shape requirements as is the case with the initially cited cylindrical roller tappets. As a rule, these roller tappets are mounted in their longitudinal guides with a guide lash of just a few micrometers, so that a deformation of the housing, generally configured with thin walls in the region of the roller, would lead to an impermissibly large non-circularity of the housing due to the radially widened reception bore resulting from the calking of the bearing pin.
As proposed in the cited document U.S. Pat. No. 5,385,124, it is certainly possible to circumvent this chain of drawbacks by using an axially uniformly core-hardened bearing pin whose front ends are not deformed and which is float-mounted in its reception bore while being fixed axially through positive engagement by circlips. Although the bearing pin can be economically manufactured with regard to the simplified heat treatment, there still remains, even in this case, a cost-increasing extra expenditure for the circlips and their assembly as well as for making the undercuts in the housing for receiving the circlips.
A method of the pre-cited type in which the bearing pin is widened at its ends in a completely core-hardened state for fixing it by positive engagement in the housing is known from the document DE 10 2006 054 406 A1 which is considered to be species-defining. In this method known under the name of radial spot riveting, the radial widening of the pin ends is effected through a riveting die whose longitudinal axis traverses a loop line wobbling within a circular cone which is concentric to the bearing pin. Due to the high contact forces, the material of the front ends of the bearing pin is successively deformed in the course of the wobbling movement. An important drawback of this method, however, results from the comparatively long working time which is required for traversing the loop line and thus counteracts short cycle times for manufacturing the lift transmitting component.